The cystic fibrosis transmembrane conductance regulator protein (CFTR) is a cAMP-activated chloride (Cl−) channel expressed in epithelial cells in mammalian airways, intestine, pancreas and testis. CFTR is the chloride-channel responsible for cAMP-mediated Cl− secretion. Hormones, such as a β-adrenergic agonist, or a toxin, such as cholera toxin, leads to an increase in cAMP, activation of cAMP-dependent protein kinase, and phosphorylation of the CFTR Cl− channel, which causes the channel to open. An increase in cell Ca2+ can also activate different apical membrane channels. Phosphorylation by protein kinase C can either open or shut Cl− channels in the apical membrane. CFTR is predominantly located in epithelia where it provides a pathway for the movement of Cl− ions across the apical membrane and a key point at which to regulate the rate of transepithelial salt and water transport. CFTR chloride channel function is associated with a wide spectrum of disease, including cystic fibrosis (CF) and with some forms of male infertility, polycystic kidney disease and secretory diarrhea.
The hereditary lethal disease cystic fibrosis (CF) is caused by mutations in CFTR. Observations in human cystic fibrosis (CF) patients and CF mouse models indicate the functional importance of CFTR in intestinal and pancreatic fluid transport, as well as in male fertility (Grubb et al., 1999, Physiol. Rev. 79:S193-S214; Wong, P. Y., 1997, Mol. Hum. Reprod. 4:107-110). However, the mechanisms remain unclear by which defective CFTR produces airway disease, which is the principal cause of morbidity and mortality in CF (Pilewski et al., 1999, Physiol. Rev. 79:S215-S255). Major difficulties in understanding airway disease in CF include the inadequacy of CF mouse models, which manifest little or no airway disease, the lack of large animal models of CF, and the limited availability of human CF airways that have not been damaged by chronic infection and inflammation. High-affinity, CFTR-selective inhibitors have not been available to study airway disease mechanisms in CF or to create the CF phenotype in large animal models.
High-affinity CFTR inhibitors also have clinical applications in the therapy of secretory diarrheas and cystic kidney disease, and in inhibiting male fertility. The compounds diphenylamine-2-carboxylate (DPC) and 5-nitro-2-(3-phenylpropyl-amino)benzoate (NPPB) inhibit CFTR at high concentrations but are non-specific in their inhibitory action (Cabantchik et al., 1992, Am. J. Physiol. 262:C803-C827; McDonough et al., 1994, Neuron 13:623-634; Schultz et al., 1999, Physiol. Rev. 79:S109-S144). The best CFTR inhibitor available for electrophysiological and other cell-based studies, glibenclamide, is used at concentrations of >100 μM (Sheppard et al., 1992, J. Gen. Physiol. 100:573-591; Hongre et al, 1994, Pflugers Arch. 426:284-287). However, at this concentration glibenclamide also inhibits other Cl− transporters as well as K+ channels (Edwards et al., 1993, Br. J. Pharmacol. 110:1280-1281; Rabe et al., 1995, Pflugers Arch. 429:659-662; Yamazaki et al., 1997, Circ. Res. 81:101-109). Effective small molecule inhibitors of other ion transport proteins are known, but no small molecules with specific CFTR inhibitory ability suitable for therapy of secretory diseases have been available.
There is accordingly a need for CFTR inhibitor compounds and methods of using such compounds for development of animal models useful in the study and treatment of CF and the treatment and control of secretory disorders. The present invention addresses these needs, as well as others, and overcomes deficiencies found in the background art.